8khz polling rate keypad, uses STM32F405 and USB3300, powered by QMK.
This project is just a prototype, cases, plates and other keyboard components are not included.
The code can be found on my Fork.
STM32f405/7xx should comes with a built-in bootloader, but sadly it doesn't seem to work on USB HS interface, if someone uses the default bootloader, he has to manually switch to FS port to upload firmware, then switch back to HS port to use his keyboard.
To address the issue, we can use a mux chip with tinyuf2 bootloader to automatically do that trick, then you don't bother switching port.
The mux chip we used here is TS3USB221, connect its 'S' pin to B14 of STM32. In normal operation, pull the pin to low to select HS interface, in bootloader mode, write this pin to high to select FS interface.
The tinyuf2 bootloader code can be found here, if you wish to change B14 to other pin, you can modify it in board.h.
//--------------------------------------------------------------------+
// Custom GPIO, used for USB mux
//--------------------------------------------------------------------+
#define CUSTOM_GPIO_PORT GPIOB
#define CUSTOM_GPIO_PIN GPIO_PIN_14